Joe Pistone (Johnny Depp) is an FBI mole who integrates himself into the Mafia pecking order by posing as jewel man Donnie Brasco. He finds his loyalties divided when Lefty Ruggiero, a jaded hit man, takes him on as a protégé and places real trust in him. The two men form a friendship–and a criminal partnership–that jeopardizes Brascos mission and obscures the boundaries between the law and the underworld.